1. Field of the Invention
The present invention relates to a variable speed switch which is mounted to an electric power tool etc. and capable of outputting an electric signal for increasing and decreasing the amount of an electric power supplied to a motor of the electric power tool in proportion to the displacement amount of a switch operating portion. The present invention further relates to an electric power tool provided with the above variable speed switch and further provided with a wake-up switch configured to apply voltage to a control circuit of the motor to work the control circuit.
2. Description of the Related Art
Japanese Patent Application Laid-Open No. 2003-260675 discloses a variable speed switch in the prior art.
As shown in FIG. 12, a variable speed switch 100 according to the above-mentioned publication includes a trigger 102 operated by being pulled with a finger, and a switch main body portion 105 provided with a slide-type variable resistor (not shown) interlocked with the pulling operation of the trigger 102. The trigger 102 is provided with a support shaft 103 protruding rearwards (to the right as seen in the drawing), and the support shaft 103 is supported by a bearing 105j of the switch main body portion 105 so as to be slidable in the axial direction. Further, inside the switch main body portion 105, there is provided a spring 105b biased to return the trigger 102 to the original position (a leftward end position).
When the trigger is pulled against the force of the spring 105b, the variable speed switch 100 is turned on, resulting in a reduction in resistance value as the amount by which the trigger 102 is pulled increases. And, as a result of the reduction in the resistance value of the variable speed switch 100, the amount of electric power supplied to the motor of the electric power tool increases, resulting in an increase in the rotational speed of the motor. When the trigger 102 is returned to the original position by the force of the spring 105b, the variable speed switch 100 is turned off, and the amount of electric power supplied to the motor of the electric power tool is reduced to zero, thereby stopping the motor.
Generally, in order to suppress power consumption of the battery, a power source of the control circuit of the motor in an electric power tool is configured to be turned off when the electric power tool is not used. When the electric power tool is to be used, the wake-up switch is turned on, whereby voltage is applied to the control circuit, and the control circuit can work so as to increase or decrease the amount of electric power supplied to the motor in proportion to the amount by which the variable speed switch is pulled. When the amount by which the variable speed switch is pulled is reduced to zero, that is, when the finger is released from the variable speed switch, the control circuit turns off the power source thereof.
Generally, in an electric power tool as disclosed in Japanese Patent Application Laid-Open No. 2003-260675, a wake-up switch is incorporated into the variable speed switch. More specifically, as shown in FIG. 12, the variable speed switch 100 includes the trigger 102 operated by being pulled with a finger, the switch main body portion 105 provided with a slide-type variable resistor (not shown) interlocked with the trigger 102, and a wake-up switch (not shown) incorporated into the switch main body portion 105. As shown in FIG. 13, when the trigger 102 is pulled by a fixed amount L0 against the force of the spring 105b, the wake-up switch is turned on and the voltage is applied to the control circuit. When the trigger 102 is further pulled, the resistance value of the variable resistor varies in proportion to the pulling amount, and the control circuit increases or decreases the amount of electric power supplied to the motor as the resistance value varies.
However, in the variable speed switch 100 described above, the configuration is such that the resistance value of the variable resistor varies as the amount by which the trigger 102 is pulled increases or decreases, and thus it is necessary to set the movement amount (stroke) of the trigger 102 with respect to the switch main body 105 to be relatively large. This results in an increase in the size of the variable speed switch 100, and eventually the degree of freedom may be reduced when the variable speed switch 100 is incorporated into the electric power tool. Further, since the stroke of the trigger 102 with respect to the switch main body 105 is relatively large, the waterproof structure for the electric power tool with the variable speed switch 100 attached thereto may be rather complicated.
Further, in the above-described variable speed switch 100, when the trigger 102 is pulled by a fixed amount L0, the wake-up switch is turned on, and the voltage is applied to the control circuit. In case that a variable speed switch 100 is used in which the maximum pulling amount of the trigger 102 is smaller than the fixed amount L0, the wake-up switch cannot be turned on by the trigger 102 of the variable speed switch 100.
Thus, there is a need to reduce the displacement amount of the switch operation portion with respect to the switch main body, in order to improve the degree of freedom in the mounting of the variable speed switch and also to simplify a waterproof structure for the electric power tool.
Further, there is a need to provide a wake-up switch that can apply voltage to the control circuit of the motor, even when a variable speed switch is used in which the pulling amount of the trigger is small.